Thermosetting polymers systems are widely used in many applications including protective coatings, composite materials, and adhesives. Many of these systems involve the reaction of polymers or oligomers with other materials containing mutual reactive groups. For example, hydroxyl functional polymers are crosslinked with functional oligomers, or epoxy resins are crosslinked with polyfunctional amines.
The final properties of thermoset coatings are determined by the composition of the reactants used. Epoxy coatings generally exhibit good corrosion performance while polyurethane systems result in coatings having good toughness, abrasion resistance, and durability. Epoxy urethane (glycidyl carbamate) chemistry has the potential of combining epoxy and polyurethane technology into a single system and has been shown to improve toughness in epoxy-amine systems (Hsia H. C. et al., “Glycidyl-Terminated Polyurethane Modified Epoxy Resins: Mechanical Properties, adhesion Properties and Morphology”, J. Appl. Polym. Sci., 52, 1134 (1994) and Edwards, P. A. et al., “Novel Polyurethane coating Technology Through Glycidyl Carbamate Chemistry”, JCT Research, 2, 517, (2005)).
Epoxy urethane (glycidyl carbamate) group is readily synthesized from the reaction of an isocyanate with glycidol:
(Tefertiller, N. B. et al., U.S. Pat. No. 4,397,993; Edwards, P. E. et al., Synthesis and Self-Crosslinking of Glycidyl Carbamate Functional Oligomers, Polymer Preprints 2003, 44(1), 54.)
Epoxy urethane (glycidyl carbamate) functional polymers offer some unique opportunities in the formation of thermosetting polymers because the reactivity of an epoxy resin is combined with the physical properties obtained with polyurethanes. Epoxy urethane (glycidyl carbamate) functional oligomers can thermally self-crosslink and also crosslink with multifunctional amines. Kinetic experiments have shown that the glycidyl carbamate epoxy is more reactive than conventional glycidyl ether epoxides. Physical properties of the coatings are also excellent and have an excellent combination of both hardness and flexibility.
There is an increased interest in developing water-dispersible coating compositions to meet the environmental standards. The preparation of conventional polyurethane dispersions is well known in the art (Dietrich, D., Die Ang. Makromol. Chem., 1981, 98, 133-165; Kim., B. K. et al., J. Polym. Sci. Polym. Chem. Ed., 1996, Vol. 34, 1095-1104; Coogan, R. G. et al., U.S. Pat. No. 5,043,381). Waterborne polyurethane dispersions (PUD) require many process steps but yield good properties and are one of popular methods in reducing volatile organic compounds (VOCs). There are many resins used in water dispersion chemistry. For example, there are alkyd polyurethane dispersions (Dou, Z., et al., “Low VOC Polyol Alkyd Dispersion and Polyurethane Dispersions,” PCT Int. Appl. WO/2002/031021), hydroxyl functional latexes (Dvorchak, M., et al., “A new water reducible blocked polyisocyanate (NWRBP) for one component (1K) polyurethane coatings,” Proceedings of the International Waterborne, High-Solids, and Powder Coatings Symposium (2000), 27th 405-419; Escarsega, J. A., et al., “Water reducible PUR coatings for military applications,” Modern Paint and Coatings (1997), 87(7), 21, 24-26; Grunlan, M. A., et al. “Waterborne coatings with an emphasis on synthetic aspects; an overview.” ACS Symposium Series (1997), 663 (Technology for Waterborne Coatings), 1-26; Hartz, R. E., “Reaction during cure of a blocked isocyanate-epoxy resin adhesive,” Journal of Applied Polymer Science (1975), 19(3), 735, water reducible polyesters (7 Gaal, R. J., et al., “Water-reducible polyester resins and urethane coatings produced therefrom,” U.S. (2001); Page, A., et al., “Polyester resins in water-based urethanes,” Paint Ink International (1996), 9(2), 37,40; Dvorchak, M. J., et al. “Water-reducible unsaturated polyester polymers as binder for UV-curable furniture coatings,” Proceedings of the Waterborne, High-Solids, and Powder Coatings Symposium (1991), 18th 253-67), and water reducible acrylics (Venditti Wang, et al. “Synthesis and characterization of UV-Curable waterborne polyurethane-acrylate ionomers for coatings,” Journal of Applied Polymer Science (1999), 73 (844), 2869-2876); and Yang, Jian-wen et al., “Chain-extended UV-curable waterborne polyurethane-acrylate,” Gaofenzi Cailiao Kexue Yu Gongcheng (2003), 19(2), 199-202.
One of the major problems with isocyanates when mixing in polyol is that most hydroxyl functional crosslinkers are hydrophobic. In some formulations, this has been overcome by mixing resin particles (Jang, Jong Yoon et al., “Effect of process variables on molecular weight and mechanical properties of water-based polyurethane dispersion,” Colloids and Surfaces, A: Physicochemical and Engineering Aspects (2002), 196(2-3), 135-143; Guenduez, G. et al., “Structure-Property Study of Waterborne Polyurethane Coatings with Different Hydrophilic Contents and Polyols,” Journal of Dispersion Science and Technology (2004), 25(2), 217-228) to protect the reaction from hydrolysis (Qu, Jinqing et al., “Syntheses of high solid content waterborne polyurethane dispersion,” Huagong Xucbao (2003), 54(6), 868-871) or by isocyanate monomer selection (Song, Xiao-hui et al., “Effect of PEG molecular weight in hydrophilic segment on the crystallization of cast film of waterborne polyurethane,” Xiamen Daxue Xuebao, Ziran Kexueban (2002), 41(4), 463-467). Two component systems are usually formulated with the isocyanate in excess to alcohol, by using a ratio of isocyanates to alcohol of 2:1 (over-indexing). These systems require more isocyanate to be used due to competing reactions with water. One way to lessen isocyanate reactivity with water is to increase molecular weight by building the prepolymer (Jang, Jong Yoon et al., “Effect of process variables on molecular weight and mechanical properties of water-based polyurethane dispersion,” Colloids and Surfaces, A: Physicochemical and Engineering Aspects,” (2002), 196(2-3), 135-143; Webb, D. D. “Urethane systems reactivity measurement,” Journal of Cellular Plastics (1985), 21(3), 208-12). The dominant isocyanate reaction is with an alcohol group (Illger, H. W., et al. “Reaction kinetics study of high resilient polyurethane foams,” Polyurethanes World Congr. Proc. FSK/SPI (1987), 305-10. Publisher: Technomic, Lancaster, Pa.).
There is currently a great need for low or near zero VOC (volatile organic content) systems in developing waterborne resin technology. Therefore, it is advantageous to provide waterborne polyurethane dispersions that provide the performance currently required by the industries with excellent combination of higher reactivity and physical properties of epoxy and polyurethane technology. It would be also desirable that the coating compositions can be dispersed in water with or without added surfactants to form a dispersion containing no volatile organic solvent.